The present invention relates to implants, especially stents, primarily for introduction into blood vessels, but which are also useful for introduction into other body lumens, which have a coating of a biocompatible hydrogel polymer, used as a reservoir from which drugs are delivered direct to the wall of the vessel in which the stent is positioned.
In our earlier WO-A-0101957 which was not published at the priority date hereof, we describe stents with coatings of biocompatible crosslinked polymers, which are swollen in drug containing solutions immediately before delivery into a patient. Drug is absorbed into the swollen hydrogel, and is released over extended periods of time from the implanted stent. The system described in those applications has been approved for marketing in Europe for use with drugs having molecular weights up to 1200D. Examples of such drugs include dipyridamole, dicloxacillin, vitamin B12 and angiopeptin.
In our earlier application number WO-A-9822516, we describe polymers formed from ethylenically unsaturated monomers including a cationic monomer and a zwitterionic monomer, useful for providing biocompatible coatings on various substrates. The cationic polymer attracts anionic mucopolysaccharide. A stent coated with the polymer may be used as a scavenging device to remove systemic heparin from the circulation of a patient. Alternatively, it is suggested that the device may be preloaded with, for instance, heparin to allow extended release of the drug into a circulation from an implanted stent.
In EP-A0809999, heparin is covalently bound to a stent using the Carmeda CH5 heparin coating system.
Angiogenic compounds have been delivered from stents to treat stenotic lesions. In WO-A-97/47253, for instance, angiogenic compounds are delivered following radiation treatment of the heart. Delivery may be from a stent coated with a polymer.
In U.S. Pat. No. 5,954,706 an anionic hydrogel is coated on to a stent, a monovalently cationic compound, such as a benzalkonium compound, is coated over the hydrogel and heparin is contacted and electrostatically bound to the cationic compound.
Sense and anti-sense DNA have been delivered from stents, for instance in WO-A-98/15575. The DNA may encode an angiogenic protein.
In U.S. Pat. No. 5,674,192 nucleic acids and monoclonal antibodies delivered by squeezing them from a swollen hydrogel coating on a balloon catheter. The nucleic acids may be antisense oligonucleotides or viral vectors. The hydrogel may be a polycarboxylic acid such as polyacrylic acid. Nucleic acid is delivered to cells of the vessel wall.
A new implant according to the invention has a coating on its external surface comprising:
a) a crosslinked, water swellable polymer matrix having a dry thickness of at least 0.1 xcexcm, and
b) a pharmaceutically active compound
in which the polymer has pendant zwitterionic groups and pendant cationic groups.
The implant is preferably a stent.
The invention is of particular utility for delivering pharmaceutically active compounds which are anionic under physiological conditions. The invention is also of particular value for higher molecular weight active compounds, especially having molecular weights of more than 1000D, more preferably more than 1200D, for instance 5000D or more.
The pharmaceutical active may be a protein, for instance an antibody or fragment thereof. Such compounds are usually and preferably in this invention anionically charged in physiological environments. The invention is of particular value for active compounds comprised of nucleic acids. The nucleic acids may be DNA or RNA, and may be linear or circular, single or double stranded. The nucleic acid may encode a pharmaceutically useful polypeptide or protein, or it may be an anti-sense oligo-nucleotide, used to control the gene of interest in the cell to which the nucleic acid is delivered. A nucleic acid encoding a useful polypeptide or protein may include control regions, or other sequences to allow expression of the gene and/or its delivery into the cell and/or transport of the protein to its target. Oligo nucleotides conjugated to other actives eg for targeting purposes, are also usefully delivered by this invention.
One particularly interesting class of gene delivered by the invention encodes angiogenic factors, such as vascular endothelial growth factors or fibroblast growth factors, or platelet derived growth factors. Suitable control sequences may direct expression in smooth muscle cells, specifically. For instance the control sequences may be as described in WO-A-98/15575. Oligonucleotides which may be used in the present invention have, for instance, at least 5 bases, preferably at least 15 bases.
According to a second aspect of the invention, a new implant has a coating on its external surface comprising:
a) a crosslinked, biostable polymer matrix and
b) a pharmaceutically useful nucleic acid,
in which the polymer has pendant zwitterionic groups and pendant cationic groups.
According to a third aspect of the invention, a new implant having a coating on its external surface comprising:
a) a cross-linked, biostable polymer and
b) a pharmaceutically active compound which is a protein which is anionically charged at physiological pH in which the polymer has pendant zwitterionic groups and pendant cationic groups.
In the second and third aspects it is preferred, thought not essential for the polymer matrix to have a dry thickness of at least 0.1 xcexcm. Furthermore it is preferred but not essential for the polymer matrix to be water swellable. We have found that anionic actives such as nucleic acid and proteins, especially those having molecular weights above 1 KD, primarily become adsorbed at the surface of a polymer having cationic groups and zwitterionic groups, with little being adsorbed into the body of the polymer. For this reason the swellability and the thickness are of lesser importance than in the first aspect.
The implant is preferably a stent. In the rest of this specification the device is described in terms of stents, but it will be understood other implants may be substituted for stents.
The crosslinking of the polymer matrix stabilises the coating on the stent, rendering it biostable. Adjustment of the crosslink density provides some control over the extent to which the polymer swells in a swelling solvent, generally aqueous in nature. The crosslink density furthermore effects the pore size of the polymer matrix. It is believed that the pore size, in turn, effects the maximum molecular size of pharmaceutically active compounds which may be absorbed into the matrix which is of particular relevance to the first aspect of the invention. It is preferred that the polymer be formed from ethylenically unsaturated monomers including less than 20% by mole of crosslinkable monomer.
The polymer used in the present invention is preferably formed from ethylenically unsaturated monomers including
a) a zwitterionic monomer of the formula I
YBXxe2x80x83xe2x80x83I 
xe2x80x83wherein B is a bond or a straight or branched alkylene, alkylene-oxa-alkylene or alkylene-oligooxa-alkylene group, any of which optionally include one or more fluorine substituents;
X is an organic group having a zwitterionic moiety; and
Y is an ethylenically unsaturated polymerisable group;
b) a cationic monomer of the formula II
Y1B1Q1xe2x80x83xe2x80x83II 
xe2x80x83wherein B1 is a bond or a straight or branched alkylene, alkylene-oxa-alkylene or alkylene-oligooxa-alkylene group, any of which optionally includes one or more fluorine substituents;
Y1 is an ethylenically unsaturated polymerisable group; and
Q is an organic group having a cationic or cationisable moiety and C a crosslinkable monomer having the general formula IV:
Y3B3Q3xe2x80x83xe2x80x83IV 
xe2x80x83wherein B3 is a bond or a straight or branched alkylene, alkylene-oxa-alkylene or alkylene-oligooxa-alkylene group, any of which optionally includes one or more fluorine substituents;
Y3 is an ethylenically unsaturated polymerisable group; and
Q3 is an organic group having a reactive group capable of cross-linking the polymer.
Preferred reactive comonomers IV which are used to crosslink the comonomer, are those in which Q3 contains a crosslinkable cinnamyl, epoxy, xe2x80x94CHOHCH2Hal (in which Hal is a halogen atom), methylol, reactive silyl, an ethylenically unsaturated crosslinkable group, such as an acetylenic, diacetylenic, vinylic or divinylic group, or an acetoacetoxy or chloroalkyl sulfone, preferably chloroethyl sulphone, group. For optimum cross-linking a monomer including a reactive silyl group (eg a group xe2x80x94SiR43 in which each R4 is a C1-4 alkoxy group or a halogen atom) is used in combination with a is further monomer including a hydroxyl group, eg having the formula IV
Y3B3Q4xe2x80x83xe2x80x83IV 
in which Y3 and B3 are as defined in compound IV and Q4 is a hydroxyl group.
The ethylenically unsaturated monomers from which the polymer is formed may further include a termonomer of the formula III
Y2B2Q2xe2x80x83xe2x80x83III 
wherein B2 is a bond or a straight or branched alkylene, alkylene-oxa-alkylene or alkylene-oligooxa-alkylene group, any of which may optionally include one or more fluorine substituents;
Y2 is an ethylenically unsaturated polymerisable group; and
Q2 is an organic group having a hydrophobic group selected from alkyl groups having at least six carbon atoms, fluorine substituted alkyl groups and alkyl groups having at least one siloxane substituent.
For optimum film-forming and ability to coat hydrophobic surfaces, the polymers preferably contain more than 10% by mole, more preferably more than 20% by mole such termonomer.
The polymers may include diluent comonomer. Such diluent comonomer may be used in quantities up to 90 mol %, usually less than 50 mol %. Copolymerisable nonionic monomers may be used such as C1-24 alkyl(meth)acrylates, and -(meth)acrylamides, and hydroxy C1-24 alkyl(meth)acrylates and -(meth)acrylamides.
In each of the monomers I to IV the ethylenically unsaturated group is preferably selected from CHxe2x95x90CHxe2x80x94(C6H4)xe2x80x94Kxe2x80x94, CH2xe2x95x90C(R)C(O)xe2x80x94Axe2x80x94, CH2xe2x95x90C(R)xe2x80x94CH2xe2x80x94Oxe2x80x94, CH2xe2x95x90C(R)xe2x80x94CH2OC(O)xe2x80x94, CH2xe2x95x90C(R)OC(O)xe2x80x94, CH2xe2x95x90C(R)Oxe2x80x94 and CH2xe2x95x90C(R)CH2OC(O)N(R1)xe2x80x94
wherein:
R is hydrogen or a C1-C4 alkyl group;
A is xe2x80x94Oxe2x80x94 or xe2x80x94NR1xe2x80x94 where R1 is hydrogen or a C1-C4 alkyl group or R1 is xe2x80x94Bxe2x80x94X, B1Q1, B2Q2 or B3Q3, as the case may be, where B, B1, B2, B3, Q1, Q2 and Q3 and X are as defined above in the respective one of the formula I to IV and
K is a group xe2x80x94CH2)pOC(O)xe2x80x94, xe2x80x94CH2)pC(O)Oxe2x80x94, xe2x80x94CH2)pOC(O)Oxe2x80x94, xe2x80x94(CH2)pNR2xe2x80x94, xe2x80x94CH2)pNR2C(O)xe2x80x94, xe2x80x94(CH2)pC(O)NR2xe2x80x94, xe2x80x94CH2)pNR2C(O)Oxe2x80x94, xe2x80x94(CH2)pOC(O)NR2xe2x80x94, xe2x80x94(CH2)pNR2C(O)NR2xe2x80x94, (in which the groups R2 are the same or different) xe2x80x94(CH2)pOxe2x80x94, xe2x80x94(CH2)pSO3xe2x80x94, or, optionally in combination with B, a valence bond and p is from 1 to 12 and R2 is hydrogen or a C1-C4 alkyl group.
Preferably the ethylenically unsaturated groups of all monomers copolymerised together are either the acrylate type or are the styrene type (CH2xe2x95x90C(R)C(O)Axe2x80x94 or CHxe2x95x90CHxe2x80x94(C6H4)xe2x80x94Kxe2x80x94), and, most preferably each has the same formula. Preferably the groups A of acrylate type ethylenically unsaturated groups of the zwitterionic, cationic and cross-linkable monomer and any termonomer are the same and are most preferably all xe2x80x94Oxe2x80x94.
The zwitterionic group X preferably has a phosphate ester group as the anion or the thioester analogue or amide analogue or a phosphonate. The cationic moiety is preferably a quaternary ammonium group, but may be a sulphonium or phosphonium group. Preferably the cationic group is at the end of the group X distant from the group B.
Preferably X is a group of formula V 
in which the moieties X1 and X2, which are the same or different, are xe2x80x94Oxe2x80x94,xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94 or a valence bond, preferably xe2x80x94Oxe2x80x94, and W+ is a group comprising an ammonium, phosphonium or sulphonium cationic group and a group linking the anionic and cationic moieties which is preferably a C1-12-alkylene group.
Preferably W contains as cationic group an ammonium group, more preferably a quaternary ammonium group.
The group W+ may for example be a group of formula xe2x80x94W1xe2x80x94N+R63, xe2x80x94W1xe2x80x94P+R73, xe2x80x94Wxe2x80x94S+R72 or xe2x80x94W1xe2x80x94Het+ in which:
W1 is alkylene of 1 or more, preferably 26 carbon atoms optionally containing one or more ethylenically unsaturated double or triple bonds, disubstituted-aryl, alkylene aryl, aryl alkylene, or alkylene aryl alkylene, disubstituted cycloalkyl, alkylene cycloalkyl, cycloalkyl alkylene or alkylene cycloalkyl alkylene, which group W1 optionally contains one or more fluorine substituents and/or one or more functional groups; and either
the groups R6 are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, preferably methyl, or aryl, such as phenyl or two of the groups R6 together with the nitrogen atom to which they are attached form a heterocyclic ring containing from 5 to 7 atoms or the three groups R6 together with the nitrogen atom to which they are attached form a fused ring structure containing from 5 to 7 atoms in each ring, and optionally one or more of the groups R6 is substituted by a hydrophilic functional group, and
the groups R7 are the same or different and each is R6 or a group OR6, where R6 is as defined above; or
Het is an aromatic nitrogen-, phosphorus- or sulphur-, preferably nitrogen-, containing ring, for example pyridine.
Preferably W1 is a straight-chain alkylene group, most preferably 1,2-ethylene.
Preferred groups X of the formula V are groups of formula VI.
The groups of formula (VI) are: 
where the groups R8 are the same or different and each is hydrogen or C1-4 alkyl, and e is from 1 to 6.
Preferably the groups R8 are the same. It is also preferable that at least one of the groups R8 is methyl, and more preferable that the groups R8 are all methyl.
Preferably e is 2 or 3, more preferably 2.
When X is a group of formula (VI) preferably B is a group of formula xe2x80x94(CR92)xe2x80x94 or xe2x80x94CR92)2xe2x80x94, eg. xe2x80x94CH2)xe2x80x94 or xe2x80x94(CH2CH2)xe2x80x94.
Preferably the zwitterionic monomer has the general formula VII 
wherein R, A and B are defined above,
the groups R3 are the same or different and each is hydrogen C1-1 alkyl, aryl, alkaryl, aralkyl, or two or three of the groups R3 with the nitrogen atom to which they are attached form a saturated or unsaturated hetero cyclic ring, and e is 1 to 6, preferably 2 to 4.
A cationisable moiety in the group Q1 is generally a group which can easily be protonated to render it cationic, for instance which is protonated in aqueous environments at pH7.
The group Q1 of the cationic monomer is preferably a group N+R53, P+R53 or S+R52 
in which the groups R5 are the same or different and are each hydrogen, C1-4-alkyl or aryl (preferably phenyl) or two of the groups R5 together with the heteroatom to which they are attached from a saturated or unsaturated heterocyclic ring containing from 5 to 7 atoms. Preferably the group Q1 is permanently cationic, that is each R5 is other than hydrogen. Preferably Q1 is N+R53 in which each R5 is C1-4-alkyl, preferably methyl.
The relative ratios (equivalents) of zwitterionic to cationic pendant groups in the molecule of zwitterionic to cationic monomer in the range 1:100 to 100:1 (zwitterionic to ionic) preferably 1:10 to 10:1, more preferably 1:2 to 2:1.
Generally the polymers including the crosslinkable groups are coated onto the stent and crosslinked after coating. Crosslinking is generally by heating, optionally in the presence of moisture, for instance at least 40xc2x0 C., preferably at least 60xc2x0 C., for instance around 70xc2x0 C.
The pharmaceutically active compound may be loaded into the polymer matrix by being co-coated from a composition containing both the compound and cross-linkable polymer. Alternatively, and preferably, the drug is absorbed into or absorbed onto the matrix after the polymer is coated onto the stent and crosslinked thereon. This loading step is carried out by contacting the coated stent, optionally following a pre-swelling step, with a solution or dispersion of the pharmaceutically active compound in a solvent which is capable of penetrating the polymer matrix. Usually the solvent for the pharmaceutical active is a solvent which swells the polymer. Suitable loading compositions comprise water, and may additionally or alternatively comprise an alcohol. The solvent may be removed from the swollen matrix containing pharmaceutical active, but may alternatively be retained in the polymer, for instance during storage or by immediately delivering the stent to the patient.
Loading conditions are determined to achieve adequate loading of active. The temperature is selected so as to create suitable properties on the polymer. It is usually between 0 and 60xc2x0 C., preferably room temperature to about 40xc2x0 C., for instance 20 to 40xc2x0 C., most preferably around 37xc2x0 C. The solution or dispersion may contain solvents selected so as to achieve appropriate fluidity at the loading temperature.
The stent may be sterilised before or after loading, for instance by gamma-irradiation.
In order to provide adequate loading of drugs, it is preferred for the coating polymer to be at least 0.5 xcexcm, more preferably at least 1 xcexcm, thick (dry thickness). Optionally it is at least 2 xcexcm thick. The polymer coating and the pharmaceutically active compound may be coated only onto the outside of the stent, from which the pharmaceutical active is delivered directly into the wall of the vessel in which the stent is implanted. Preferably, however, the stent is provided with an overall coating of polymer, so that the lumenal surface of the stent is also provided with a coating, which may be thicker or, preferably; is thinner than the external coating.
The stent may be a shape-memory metal stent, a self-expanding stent or a balloon expandable stent. For instance, a self-expanding stent may be a rolled sheet device or a braided device. Most conveniently the stent is an etched tube balloon-expandable stent. The stent may be loaded with drug in the invention when mounted on its delivery device. An overcoat of zwitterionic polymer may be applied over the defined coating to control release in use.